Apparatus for the recovery of chemicals from black liquor



May as, 1943 A. L. HAMM 2,319,399

APPARAT S FOR THE RECOVERYVOF CHEMICALS FROM BLACK LIQUOR Filed on. 19, 1940 2 Sheets-Sheet 1 6 I .1. l 20G 23 I r W Fr I b n- /J INVENTOR u NE: a A

J ATTORNEYS May as, 1943 A. L. HAMM APPARATUS FOR. THE RECOVERY OF cHEuiIcALs FROM BLACK LIQUOR i-"ud Oct. 19. 1940 2 Sheets-Sheet INVENTOR ATI'ORNEYS Patented May 18,1943

UNITED- STATES PATENT OFFICE.

arrana'rus Fon. 'rm: ascovsm? or mmrcans mom macxnouon Alexander L. Hamm, New York, N. Y, assignor to Combustion Company, Inc., New

Engineering York, N. Y., a corporation of Delaware Application October 19, 1940, Serial N0. 361,874 I I Claims. (Cl. 122-235) This invention relates to the recovery of chemi cal and the derivin of heat fromthe black liquor of wood pulp mills, and its nature, objects and advantages will be best understood from the follow Briefly, the system ordinarily employed, comprises a smelter furnace and a waste heat boiler and its appurtenances. The black liquor, reduced to the desired density or concentration of solids, is introduced into the furnace, wherein it is evaporated to substantial dryness, the solid matter collected on the hearth, of the smelter where reduction takes place. The chemical thus recovered runs off in molten state. Air is admitted to the fuel bed in an amount sufficient to maintain a reducing I atmosphere. .The combustibles in the gases rising from the fuel bed are burned, for which purpose additional air is admitted above the fuel bed. The smelter: furnace is lined with steam generating tubes connected into the circulation of the waste heat boiler proper. Heat which would otherwise be lost is recovered in the generation of steam.

There is of course chemical in vaporized form in the fuel and flamestream and waste gases. mostly sublimed sodium sulphate and sodium carbonate. Due to the absorption of heat by the heat absorbing surface of the boiler unit, the vaporized chemical is condensed. The globules or particles of condensed chemical occasion difflculties in the banks of tubes of theboiler, partlcularly at the place where the gas stream in which they are carried enters the first boiler pass at right angles to the boiler tubes. The globules impinge upon, adhere to and build up on the tubes suiiiciently to cause them to stick together as they contact with one another in space, thus causing them to agglomerate into larger particles which gravitate to the fuel bed. While this is an impovement upon the first way described,

it is nevertheless still necessary from time to time to shut down for the removal of deposit (about entrance into the first boilerpass, provided that substantial impingement of the gases upon the surfaces employed for that purpose is avoided, and

that this can be done economically and practically, and without interfering with self-sustaining operation of the unit. By cooling the gases across the tubes at right angles and forcibly impinge. By avoiding substantial impingement of Y the gases and entrained particles upon the cool- Attempts have been made heretofore to overcome this dimculty. One way employed has been to locate a number of tubes in advance of the boiler pass substantially 'at-right angles to the 'line of gas flow,functioningafter the fashion ofthe slagging tube's'so, frequently employed in advance of the'boil'er tubes inpulverized fuel burning equipment. While this arrangement reduces the amount ofcarryover into and minimizes difficulties in. the boiler tube. banks, it, in effect, only shifts the' seat of the difficulty to the so-called sl s nfi tubes, and it is still necessary to shut down the installation for removal of the ing'surfaces employed for that purpose, even though the particles be molten, sticking and building up on said surfaces is avoided. All deposit on all surfaces is thus either powder or of a powdery and friable nature, such that the de-. posit can be easily removed from the surfaces by the-use of soot blowers and hand lances, without the need of shut-down.

In the drawings: Figure 1 is a more or less diagrammatic vertical section through a. smelter and boiler for practicing the invention; Figure.2 is a section taken on the line 2-2 of Figure 1, oifan enlarged scale;

Figure 3 is a section taken on, the line 3-3 o I Figure l, on an enlarged scale, and c Figure ,4 is a section illustrating a modification of the water walls employed in carrying out the invention; r D

7 Referring now to Figure l, the reference character A denotes the smelter furnace, the four walls of which are lined with exposed, one inch finned, three inch tubes I, spaced on flve and one-half inch centers, connected with the boiler proper!) for circulation, as will further appear. Immediately above the smelter furnace 'A is a chamber 13 to. the rear of which is the boiler proper C. the appurtenances of which (such as economizer, air preheater and the like) are not shown. The furnace chamber A and the chamber B are of substantially equal height, and have an overall height of sixty feet. The tubes I are approximately thirty feet long in the installation shown.

The black liquor evaporated to the desired density, approximately 65% to 70% solids, is introduced into the furnace chamber by the nozzles 8, the black liquor being supplied to the nozzles at a pressure from about 75 to 100 pounds per square inch and at a temperature of from 230 to 240 F., as described in U. S. Letters Patent No. 2,213,052, issued August 27, 1940. Owing to the reduction in pressure at the spray nozzles, some of the moisture contained in the sprayed particles flashes into steam, thus further increasing the density of the particles. The sprayed particles gravitate in counterfiow with the rising flame and gas stream from the smelting zone and are dried in space to substantial dryness. The dried particles collect on the hearth in the form of a bed of fuel 9. Preheated air for reduction is admitted through the fuel bed by means of the air nozzles I0, in an amount sufficient to maintain a reducing atmosphere in the fuel bed. The chemical flows outin molten form from the hearth. The combustibles in the gases rising from the fuel bed are burned, for' which purpose additional preheated air is admitted above the fuel bed by means of the air nozzles II, preferably downwardly inclined. Combustion under normal conditions of operation is usually completed at about a point marked I2. (Except in starting, the installation is self-sustaining, i. e., no extraneous fuel is required.)

The finned tubes 1 in effect constitute a continuous metallic wall lining the interior of the furnace and the inner face of which is exposed to radiant heat. The heat absorbed by the exposed surfaces is sufficient to lower the temperature' of the gases leaving the top of the chamber A and entering the bottom of the chamber B to approximately 2000 F., well above the melting point of the chemicals. These two chambers open into one another at the level of the headers I3 and I3a into which the upper ends of the tubes 'l, respectively constituting the side and front walls of the inner walls of the furnace are expanded.

Referring now to the boiler proper, this comprises a steam and water drum I4, a mud drum I5 and connecting banks of upright tubes I6 and II, the tubes of the rows of each bank being staggered as indicated in Figure 2. The banks are baflied to provide vertical passes, the entrance to the first pass being below the steam and water drum I4. The front baflie is preferably formed by providing the front row of tubes I6a of the first bank with one inch fins I8. These tubes are three inches in diameter and are set on six inch centers, the gap between adjacent fins I8 being closed by the members I9. These tubes, the fins, and the closure members thus not only constitute a baille for the first bank of tubes but also the rear wall of the chamber B.

Immediately in advance of the tubes I6a there is a vertically disposed superheater 20, suspended from above the boiler setting as indicated. The superheater tubes are one and flve-eighths inch tubes, spaced on five and one-eighth inch centers in one direction and on six inch centers in a direction at right angles thereto. To guide and position the superheater unit at the rear, the tubes I6a are provided with lugs 2 I. In order to edges of the bends of the superheater tubes).

guide and support the superheater unit at the front, a row of similar tubes 22 on six inch centers, extend upwardly and forwardly from the mud drum I5 and then vertically to the drum 23 which is connected to the steam and water drum I! by the circulator tubes 24. The side .walls of the chamber B are lined with one inch finned, three inch tubes 25 set on five and one-eighth inch centers, some of them connecting directly with the drum 23 and the remainder with the headers 26 and 21, said tubes rising from the headers I3. The headers 26 and 21 are connected with the drum 23. The front wall for the chamber B is also lined with similar finned tubes 28 which rise from the headers I3a and are bent at the top to connect with thedrum 23. Except for the two rear corners, it will be seen that the chamber B is lined with a substantially continuous metallic wall, the inner face of which is exposed to radiant heat.

The gases in rising from the furnace A at a temperature of about 2000 F. and through the chamber B flow in a direction parallel to the heat absorbing surfaces of the chamber, so that there is no forcible impingement .(except only on the inclined portions of the tubes-and the lower Hence, the deposit thereon is powdery and friable in nature, and is easily removed. Nevertheless the amount of heat absorbing surface in the chamber B is sufficient to lower the temperature of the gases and entrained particles to the point at which (approximately 1200 F., substantially belowthe melting point of the chemical) the particles do not stick to the boiler tubes and build up, despite the forcible impingement of the gases and particles at the point where they flow across the tubes at right angles. Thus the deposit on the boiler tubes remains in easily removable form. Moreover, the self-sustaining operation of the unit is not interfered with despite the large amount of radiant heat surface; and the cost of installation is less than that of some other types now on the market of the same capacity,

It should here be added that the furnace shown .has a horizontal depth of nine and one-half feet and a width of twenty feet, and that the chamber B is about the same size. From these and other dimensions given the number of the various tubes, their length,,and the surface presented,

can be readily determined. The installation shown .is capable of handling 600,000 pounds of dry solids in the liquor per twenty-four hour day.

Referring to Figure 4, I have there illustrated an alternate form of water wall. The tubes are not finned and are practically in abutment with one another.

It is to be understood that a suitable downcomer means leads from the mud drum to the lower headers of the water walls of the furnace.

No dimculty is encountered with deposit on the tubes 1, not only because of parallel flow of the flame and gas stream, but also because the temperature is sufflciently high to cause the deposit to melt and run down after having built up a slight amount. I

The black liquor is normally fed to the furnace at a substantially uniform rate, determined by the desired capacity ofthe installation. In

the installation shown, there is a superheater.

boiler, and other tubes within the chamber and upper loops lie outside the boiler setting, and therefore not subjected to gas flow.

I claim: 1. In a self-sustaining system for recovering chemical and generating steam from the black liquor of wood pulp mills, a smelter furnace into which the black liquor is sprayed, a chamber thereabove and successively arranged with respect thereto as to gas flow, a boiler successively arranged with respect to the chamber as to gas flow, closely spaced exposed tubes lining said furnace, closely spaced exposed tubes lining the walls of said chamber, said chamber having an opening at the upper part thereof through which the gases flow laterally into the tubebank of the boiler, and other tubes within the chamber and in advance of the boiler, all of said tubes being connected with the boiler and the amount of exposed surface of the said tubes being suificient to lower the temperature of the gases before entering the boiler at all regular self-sustaining rates of operation to approximately 1200 F., and the tubes lining and in the chamber being so disposed that the gases have parallel flow therewith.

2. In a. self-sustaining system for recovering chemical and generating steam from the black liquor of wood pulp mills, a smelter furnace into which the black liquor is sprayed, a chamber thereabove and successively arranged with respect thereto as to gas flow. a boiler successively arranged with respect to the chamber as to gas flow, closely spaced exposed tubeslining said furnace, closely spaced exposed tubes lining the walls of said chamber, said chamber having an opening at the upper part thereof through which the gases flow laterally into the tube bank of the boiler, and other tubes within the chamber and in advance of the boiler, all of said tubes being connected with the boiler and the amount ofexposed surface of the said tubes being sufficient to lower the temperature of the gases before entering the boiler at all regular self-sustaining rates of operation to approximately 1200 F., and the tubes lining and in the chamber being so disposed that the gases have parallel flow therewith, the furnace and the chamber being of substantially the same dimension.

3. Ina self-sustaining system for recovering chemical and generating steam from the black liquor oi wood pulp mills, a smelter furnace into which the black liquor is sprayed, a chamber thereabove and successively arranged 'with respect thereto as to gas-flow, a boiler successively arranged with respect to the chamber as to gas flow, closely spaced exposed tubes lining said furnace, closely spaced exposed tubes lining the walls of said chamber, said chamber having an opening at the upper part thereof through which the gases flow laterally intoithe tube bank of the in advance of the boiler, all of said tubes being connected with the boiler and the amount of exposed surface of the said tubes being suillcient to lower the temperature of the gases before entering the boiler at all regular self-sustaining rates of operation to approximately 120D F., and the tubes lining and in the chamber being so disposed that the gases have parallel now therewith, the furnace and the chamber being of substantially the same dimension, and the furnace being of such height that combustion is substantially completed therein.

4. In a self-sustaining system for recovering chemical and generating steam from the black liquor of wood pulp mills, a smelter furnace into which the black liquor is sprayed, a chamber thereabove and successively arranged with respect thereto as to gas flow, a boiler successively arranged with respect to the chamber as to gas flow, closely spaced exposed tubes lining said furnace, closely spaced exposed tubes lining the walls of said chamber, said chamber having an opening at the upper part thereof through which the gases flow laterally into the tube bank of the boiler and other tubes within. the chamber and in advance of the boiler, all of said tubes being connected with the boiler and the amount of exposed surface of the tubes lining the furnace being sufficient to lower the temperature of the leaving gases to approximately 2000 F., and the amount of exposed surface of the tubes lining and within the chamber being suiflcient to lower the temperature of the leaving gases,. at all regular selfsustaining rates of operation to approximately 1200 F. v

5. In a self-sustaining system for recovering chemical and generating steam from the black ber, said chamber having an opening at the upper part thereof through which the gases flow laterally into the tube bank of the boiler, and other tubes within the chamber and in advance of the boiler, all of said tubes being connected with the boiler, the amount of exposed surface of the said tubes being sufllcient to lower the temperature of the gases before entering the boiler to approximately 1200' a. at all regular self-sustaining rates of operation and the tubes lining and in the chamber being so disposed that gases have parallel 'ilow therewith.

, AIJKANDIB L. mum. 

